In the design of large superconducting coils, such as the SMES (Superconducting Magnetic Energy Storage) coil, the superconductor must be mechanically supported in a thermally and electrically conducting structure. (The superconducting cable is typically comprised of a number of superconducting strands joined to a high purity aluminum stabilizer.) Protection of the SMES coil in the event of a propagating quench depends upon removal of the helium from the coil in a short period of time, and dissipation of the stored electrical energy as heat in the superconducting cable and its support structure, without excessive temperature rise, which could damage coil components. As the superconducting strands go normal (in the event of a quench), current begins to transfer into the stabilizer and the conductor support structure, and heat is generated proportional to the resistivities of the various conductors and the square of the current. The ability to protect the SMES superconducting cable and coil structure in the event of such a quench thus requires a very low electrical and thermal impedance between the superconducting cable and the supporting structure. Clearly, it is very important in the design of such coils to retain the superconducting cable against the coil structure in such a way as to maintain very good thermal and electrical contact.
Furthermore, while the cable is being wound against the structure, it needs to be retained against the possibility of coming out of its slot during the winding process; this is particularly true in the case of a rippled coil design. Because of the large number of coil structure segments required for a large coil such as SMES (approximately 40,000), one cannot afford to do complex machining operations to prepare each coil structure segment for the required cable retainers. Thus, the retainer and coil structure segment machining must both be kept very simple to reduce total costs.
Many retention schemes have been proposed. Most of the proposed schemes require attachment hardware (screws, pins, tie-wires, etc.). Because of this hardware, most of the proposed retention schemes cannot be easily removed after additional turns are wound on the coil, without some coil disassembly to acquire access to the hardware.
The present invention provides retention of the cable in the coil structure segments which is simple, removable without coil disassembly, and inexpensive. It is easy to install and remove, does not require complex preparation of the coil structure segments, and requires no attachment hardware.